Add index selection for `output_hidden_states`

[hlky]

What does this PR do?

This PR adds index selection for output_hidden_states by allowing a list of indices to be passed. In this initial version only clip is modified, note that models that copy from clip currently have some docstrings changed due to check_copies, after an initial review I'll apply the changes to those models, eventually these changes can be applied to all models.

Internally output_hidden_states normalises negative indices.

The order of indices supplied to output_hidden_states is maintained in hidden_states output and duplicate indices are supported, this is required for vipllama and the tests for vipllama respectively.

The usage of output_hidden_states in llava and other versions is updated with the exception of llava_onevision as this model uses siglip, so it will be updated when the changes from clip are applied to siglip. I looked at the checkpoints listed in the examples for other llava versions and they all appear to use clip.

Note the changes in vipllava also required reversed due to the order of selected indices -2, -5, -8, -11 and 6. vipllava needs some special handling, specifically because the test case uses 0, 0, 1, 1, 0 as the selected indices.

The result of these changes is increased memory efficiency.

Fixes #33698

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag members/contributors who may be interested in your PR. cc @amyeroberts

[LysandreJik]

cc @qubvel or @molbap for a first review :)